Alternating current and direct current integrated cable current sensor and 10KV cable insulation aging monitoring method

Abstract

The invention belongs to the technical field of power transmission and distribution of a power system, and discloses an alternating current and direct current integrated cable current sensor and a 10KV cable insulation aging monitoring method. A cable alternating current signal acquisition module used for acquiring cable alternating current signals and a cable direct current signal acquisition module used for acquiring cable direct current signals are arranged in the sensor body, the cable insulation transient aging degree is judged according to the cable alternating current signals, and the cable insulation steady-state aging degree is judged according to the cable direct current signals. The two modules are designed in an independent modularization mode, the sensor utilizes alternating-current and direct-current signal monitoring fusion processing and combines the characteristic that the relation between electric signals at the head end and the tail end of a cable and local aging parameters has high nonlinearity, local aging position information can be effectively extracted, and accurate prediction of multiple aging characteristics is achieved. The sensor is not limited by a smooth change section of insulation electrical parameters, and can accurately position a local aging section of the cable in real time.

Description

Technical Field

[0001] The invention belongs to the technical field of power transmission and distribution of electric power systems, and in particular relates to an AC / DC integrated cable current sensor and a 10KV cable insulation aging monitoring method. Background Art

[0002] Cables are a vital part of urban power transmission. With the continuous improvement of economic level, urban overhead lines are gradually replaced by underground cables and internal pipeline cables. Cables have good mechanical and electrical properties. Most of the failures are caused by the aging of the insulation layer. There are many factors that affect aging, such as the cable material itself, the external operating environment, and human or foreign body damage. Each factor or multiple factors together will cause different degrees of cable aging. According to the stress that causes cable insulation aging, it can be roughly divided into thermal aging, electrical aging, water aging, chemical corrosion, mechanical aging, etc., but the root cause is high temperature heating, which is the main inducing factor for thermal aging and insulation aging caused by continuous high temperature.

[0003] Due to the long distance of the distribution cable laying section and the limited underground space, it is difficult for the operation and maintenance personnel to enter the lower end to check the specific fault node. They can only rely on the node fault information to be transmitted back to the background, and the relative position is calculated through data transmission and attenuation model. However, many fault location methods are not accurate, which makes it difficult for the operation and maintenance personnel to determine the precise fault location, which has a great impact on fault maintenance. If there is a large error, it will also increase the operation and maintenance cost. Therefore, the fault location method of the distribution cable is worth studying. On the basis of evaluating the overall insulation condition of the cable, further locating the local aging section of the cable will help to achieve targeted maintenance, thereby reducing the system operation and maintenance cost. However, there are few studies on the real-time location method of local aging of cable insulation. Most of the existing studies rely on traveling wave injection. When the traveling wave injection method is for the smooth change section of the insulation electrical parameters, it is difficult to generate a reflection signal of sufficient strength for positioning because there is no obvious impedance discontinuity point, resulting in the inability to locate the local aging section of the cable with smooth changes in insulation electrical parameters in real time.

[0004] It can be seen that the existing monitoring method is difficult to generate a reflection signal of sufficient strength for positioning the smoothly changing section of the insulation electrical parameters, resulting in the inability to perform real-time positioning of the local aging section of the cable where the insulation electrical parameters change smoothly. Summary of the invention

[0005] The present invention provides an integrated AC / DC cable current sensor and a 10KV cable insulation aging monitoring method to solve the technical problem that in the existing monitoring method, it is difficult to generate a reflection signal of sufficient strength for positioning the smoothly changing section of the insulation electrical parameters, resulting in the inability to perform real-time positioning of the local aging section of the cable with smoothly changing insulation electrical parameters.

[0006] In order to achieve the above object, the present invention adopts the following technical contents: An AC / DC integrated cable current sensor comprises a sensor body and a cable AC signal acquisition module and a cable DC signal acquisition module arranged in the sensor body; The cable AC signal acquisition module is used to collect the cable AC signal to determine the transient aging degree of the cable insulation according to the sudden change in the current amplitude of the cable AC signal; The cable DC signal acquisition module is used to acquire the cable DC signal to determine the steady-state aging degree of the cable insulation according to the cable DC signal; The cable AC signal acquisition module and the cable DC signal acquisition module share a sampling input terminal, and the collected cable AC signal and cable DC signal are output independently.

[0007] Furthermore, the sensor body includes a coil and a conditioning module; the receiving ends of the cable AC signal acquisition module and the cable DC signal acquisition module are respectively connected to the coil, and the output ends are respectively connected to the conditioning modules; the conditioning module is used to condition and output the collected cable AC signal and cable DC signal.

[0008] Furthermore, the coil adopts a double-layer structure; wherein the inner coil is connected to the cable AC signal acquisition module, responsible for acquiring the cable AC signal generated by the cable connector; the outer coil is connected to the cable DC signal acquisition module, responsible for acquiring the cable DC signal generated by the cable injection signal; the coil is made of iron-based microcrystalline alloy or Permalloy material.

[0009] Furthermore, the cable AC signal acquisition module adopts a Hall sensing and sampling chip, which is arranged on the top of the inner coil; the cable DC signal acquisition module adopts a TMR chip, which is electrically connected to the outer coil.

[0010] Furthermore, the Hall sensing and sampling chip is made of GaAs material and uses THS119 chip; The TMR chip adopts MAGIC2001 electromagnetic chip.

[0011] Further, the conditioning module includes a temperature compensation circuit, a signal conditioning circuit, and an amplification and zeroing circuit; The temperature compensation circuit is used to adjust the operational amplifier parameters according to the ambient temperature to compensate for the sensitivity of the TMR chip; The signal conditioning circuit includes an AC component conditioning circuit connected to the Hall sensing and sampling chip and a DC component conditioning circuit connected to the TMR chip, which is used to improve the spread spectrum communication distance; The amplification and zeroing circuit is used to amplify the signals collected by the Hall sensing and sampling chip and the TMR chip and to zero the TMR chip.

[0012] Furthermore, the sensor uses an open-loop mode to monitor the cable insulation; the acquisition principle of the cable AC signal acquisition module is based on the following formula:

[0013] In the formula, is the output voltage signal; R is the Hall coefficient; I is the driving current of the Hall element; B is the magnetic field strength of the magnetic ring air gap.

[0014] A 10KV cable insulation aging monitoring method, based on the above-mentioned AC / DC integrated cable current sensor, comprises: Collect the cable AC signal of the cable insulation and judge the transient aging degree of the cable insulation according to the sudden change of current amplitude in the flow signal; The cable DC signal of the cable insulation is collected synchronously, and the steady-state aging degree of the cable insulation is determined according to the cable DC signal.

[0015] Furthermore, by injecting a common mode DC current signal source, a TMR electromagnetic detection method is used to collect the cable DC signal of the cable insulation.

[0016] Furthermore, it also includes: drawing a leakage current variation trend curve based on the output cable DC signal of the cable insulation, so as to compare and analyze the steady-state aging degree of cable insulation corresponding to different cable insulations according to the leakage current variation trend curve.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The invention provides an AC / DC integrated cable current sensor, which comprises a sensor body. A cable AC signal acquisition module for acquiring cable AC signals and a cable DC signal acquisition module for acquiring cable DC signals are arranged in the sensor body. The transient aging degree of cable insulation is judged according to the cable AC signal, and the steady-state aging degree of cable insulation is judged according to the cable DC signal. The two modules are designed independently in modular form. The sensor utilizes AC / DC signal monitoring fusion processing, and the relationship between electrical signals at both ends of the cable and local aging parameters has a highly nonlinear characteristic, so that the location information of local aging can be effectively extracted, and accurate prediction of multiple aging characteristics is achieved. The sensor is not restricted by the smooth change section of the insulation electrical parameters, and can accurately locate the local aging section of the cable in real time. The sensor has a simple structure and principle, high monitoring efficiency and accuracy, and has good popularization and application value.

[0018] Preferably, in the present invention, the sensor body includes a coil and a conditioning circuit, so that the signal acquisition and conditioning process is clearer; the direct connection between the coil and the acquisition module and the further processing of the signal by the conditioning circuit improve the efficiency and accuracy of signal acquisition.

[0019] Further preferably, in the present invention, the coil adopts a double-layer structure coil, which is optimized for AC signals and DC signals respectively, thereby improving the pertinence and sensitivity of signal acquisition; the outer shielding layer can shield and offset the large AC current through the inner coil, thereby improving the measurement accuracy of the outer tiny current; At the same time, the use of iron-based microcrystalline alloy or Permalloy material enhances the magnetic properties and stability of the coil.

[0020] Further preferably, in the present invention, the cable AC signal acquisition module adopts a Hall sensing and sampling chip, and the cable DC signal acquisition module adopts a TMR chip, which improves the accuracy and reliability of signal acquisition.

[0021] More preferably, in the present invention, the Hall sensing and sampling chip adopts the THS119 chip made of GaAs material; the TMR chip adopts the MAGIC2001 electromagnetic chip, which ensures the stable performance of the signal acquisition module and may bring additional technical advantages, such as low power consumption, high sensitivity, etc.

[0022] Further preferably, in the present invention, the conditioning module includes a temperature compensation circuit, a signal conditioning circuit, and an amplification and zeroing circuit, which further improves the accuracy and stability of signal processing; in particular, the temperature compensation circuit effectively reduces the impact of temperature on the sensitivity of the TMR chip.

[0023] Preferably, in the present invention, the cable AC signal acquisition module of the sensor realizes signal acquisition based on the Hall effect, and has the advantages of non-contact and high precision.

[0024] The present invention also provides a 10KV cable insulation aging monitoring method, which realizes comprehensive monitoring of transient and steady-state aging of cable insulation by synchronously collecting AC and DC signals of the cable. Independent modular design is adopted internally for AC and DC component detection. The method designs two output lines, and samples two analog signals respectively as a basis for platform fault judgment. The two line signals are isolated, modularized, and shielded by a design mode, which greatly reduces sampling interference. The use of the method improves the real-time and accuracy of monitoring.

[0025] Preferably, in the present invention, by injecting a common-mode DC current signal source and adopting a TMR electromagnetic detection method, the acquisition accuracy and reliability of the cable DC signal are improved; by measuring the cable insulation leakage current, the cable insulation capacitance and resistance can be monitored, and the function of accurately monitoring the DC leakage current signal of the 10kV cable online can be realized.

[0026] Preferably, the present invention also includes a step of comparing and analyzing the steady-state aging degree of cable insulation based on the leakage current change trend curve, which provides strong support for the long-term monitoring and evaluation of the cable insulation status; this helps to promptly discover potential problems and take corresponding maintenance measures. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A structural block diagram of an AC / DC integrated cable current sensor provided by an embodiment of the present invention; Figure 2 A capacitive leakage current variation trend diagram corresponding to the aging degree of a 10kV cable provided in an embodiment of the present invention; Figure 3 This is a resistive leakage current variation trend diagram corresponding to the aging degree of a 10kV cable provided in an embodiment of the present invention.

[0028] Reference numerals: DETAILED DESCRIPTION In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail in the following specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0030] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0032] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0033] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0034] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] Example 1 As mentioned in the background technology, there is currently little research on real-time positioning methods for local aging of cable insulation, and most existing research relies on traveling wave injection. However, when the traveling wave injection method is used for smoothly changing sections of insulation electrical parameters, it is difficult to generate a reflection signal of sufficient intensity for positioning because there are no obvious impedance discontinuities, resulting in the inability to perform real-time positioning of local aging sections of cables with smoothly changing insulation electrical parameters.

[0036] In order to solve the above problems, this embodiment provides an AC / DC integrated cable current sensor and a 10KV cable insulation aging monitoring method. Different from the traditional traveling wave-based method, it utilizes AC / DC signal monitoring fusion processing, combined with the highly nonlinear characteristics of the relationship between the electrical signals at both ends of the cable and the local aging parameters, and can effectively extract the location information of local aging, solving the problem of accurate prediction of multiple aging characteristics; and the use of this monitoring method can improve the accuracy of online monitoring and positioning of distribution cable insulation, and reduce the intelligence level and operation and maintenance cost of intelligent inspection of distribution cables.

[0037] The present invention is further described in detail below with reference to the accompanying drawings and embodiments: like Figure 1 As shown, this embodiment provides an AC / DC integrated cable current sensor, including a sensor body, a cable AC signal acquisition module and a cable DC signal acquisition module. The cable AC signal acquisition module and the cable DC signal acquisition module share a sampling input terminal, and the collected cable AC signal and cable DC signal are output independently, which effectively avoids the signal interference and ensures the accuracy of monitoring.

[0038] The cable AC signal acquisition module and the cable DC signal acquisition module are arranged in the housing of the sensor body; Among them, the sensor body includes a coil and a conditioning module; the receiving ends of the cable AC signal acquisition module and the cable DC signal acquisition module are respectively connected to the coil, and the output ends are respectively connected to the conditioning circuit; the conditioning module is used to condition and output the collected cable AC signal and cable DC signal.

[0039] The coil adopts a double-layer structure. The inner coil is connected to the cable AC signal acquisition module, which is responsible for collecting the cable AC signal generated by the cable joint; the outer coil is connected to the cable DC signal acquisition module, which is responsible for collecting the cable DC signal generated by the cable injection signal; this coil adopts an iron-based microcrystalline alloy or Permalloy coil.

[0040] The cable AC signal acquisition module uses a Hall sensing and sampling chip and is set at the top of the inner coil to collect the cable AC signal to determine the transient aging degree of the cable insulation based on the sudden change in the current amplitude in the cable AC signal.

[0041] The cable DC signal acquisition module adopts a TMR chip and is electrically connected to the outer coil to collect the cable DC signal so as to determine the steady-state aging degree of the cable insulation based on the cable DC signal.

[0042] In this embodiment, the conditioning module includes a temperature compensation circuit, a signal conditioning circuit, and an amplification and zeroing circuit, which are used to adjust the operational amplifier parameters according to the ambient temperature to compensate for the sensitivity of the TMR chip, improve the spread spectrum communication distance, and zero the TMR chip.

[0043] It can be seen that this sensor integrates the cable AC signal acquisition module and the cable DC signal acquisition module in the same sensor body, realizing the synchronous acquisition of AC and DC signals, and improving the comprehensiveness and accuracy of cable insulation aging monitoring. At the same time, the shared sampling input terminal but independent output ensures the flexibility and independence of signal processing, thereby reducing interference and improving monitoring accuracy; the use of this sensor is not limited by the smooth change of insulation electrical parameters, and the use of AC and DC signal monitoring fusion processing can locate the local aging section of the cable in real time.

[0044] Example 2 This embodiment provides an AC / DC integrated cable current sensor and a 10KV cable insulation aging monitoring method, which are specifically used for monitoring and analyzing the degree of aging of 10KV cable insulation. The idea behind this method is: first, under normal circumstances, the cable insulation aging characteristics can be manifested as transient and steady-state changes; transient aging is generally due to sudden changes in load current (such as fault grounding short circuit, etc.), which will produce sudden current amplitude changes in the cable AC signal, and it is judged that a transient grounding fault has occurred in the cable; secondly, the cable gradually ages during long-term operation due to factors such as the cable structure itself, the influence of the tunnel environment, and load changes. This aging process is a process accumulation, showing a gradual change feature. This is achieved by injecting a common-mode DC current signal source. , and using TMR electromagnetic detection leakage current can detect weak DC signals, so as to judge the parameters of the steady-state aging process of the cable; using the two AC and DC monitoring parameters together as the basis for judging the cable insulation aging process, it can basically holographically perceive the cable insulation operation status, and provide strong on-site data support for the cable operation control of the cable team; second, the AC current Hall monitoring is proposed, which is a non-contact measurement method. The output voltage is proportional to the magnetic field strength and has nothing to do with the rate of change of the magnetic field; from the structural point of view, the Hall current sensor is divided into closed loop and open loop. For the current status of 10kV cable monitoring, most of the current sensors are installed for the cables that have been laid, so the later installation method can only adopt the open loop mode, and the inner diameter of the magnetic coil can be customized later. The peripheral circuit of the open-loop Hall sensor is simple and the cost is relatively low, but due to its poor accuracy and linearity, slow response time, and large temperature drift, it is more suitable for detecting transient AC fault current. In order to avoid some of the above defects of the Hall sensor, this embodiment makes precise judgments in the selection of Hall component materials and magnetic material selection, with the main purpose of improving the performance of magnetic concentration and measurement linearity; more specifically, this embodiment uses the Hall effect to realize the monitoring of AC current; the Hall effect is a kind of magnetoelectric effect, and the components, circuits and systems composed based on the Hall effect are called train sensors, which are non-contact measurement sensors, and the output voltage is proportional to the magnetic field strength and has nothing to do with the rate of change of the magnetic field. Structurally, the Hall current sensor is divided into two types: closed loop and open loop. For the current status of 10kV cable monitoring, most of the installed current sensors are already laid cables, so the subsequent installation method can only adopt the open loop mode, and the inner diameter of the magnetic coil can be customized later. The open-loop Hall current sensor has a single closed magnetic circuit core with an inner diameter of d. The Hall chip is placed in the open air gap of the core, and the air gap length is L. The element can directly detect the magnetic field signal and output it as a voltage signal Vout. The proportional relationship between the output voltage and the magnetic field B is as follows:

[0045] I is the driving current of the Hall element, B is the magnetic field strength of the air gap of the magnetic ring, and R is the Hall coefficient, which is often determined by the material of the Hall element. The Hall current sensor converts the magnetic field generated by the magnetic ring aggregation around the current-carrying conductor into a voltage signal at the mV level. The open-loop Hall sensor has a simple peripheral circuit form and relatively low cost, but due to its poor accuracy and linearity, slow response time, and large temperature drift, it is more suitable for detecting transient AC fault currents. In order to avoid some of the above defects of the Hall sensor, this embodiment makes precise judgments in the selection of Hall component materials and magnetic materials, with the main purpose of improving the magnetic concentration and measurement linearity performance.

[0046] Third, the TMR DC micro-current monitoring method proposed in this embodiment evaluates the insulation characteristics of the cable by monitoring the leakage current, and evaluates the operating health of the cable from another aspect. The aging of the cable insulation is often accompanied by the change of the relative dielectric constant. During the operation of the cable, the number of gaps in the insulation will continue to increase, and the moisture and impurities in the environment are also easy to enter the gaps, so that the relative dielectric constant of the cable insulation increases. This embodiment studies the insulation aging type in which the relative dielectric constant of the insulation changes in the cable. After a large number of experimental phenomena, it is shown that by measuring the cable insulation leakage current, the cable insulation capacitance and resistance can be monitored, thereby estimating the degree of insulation aging. As the degree of aging increases, the rising trend of the insulation capacitance remains consistent over a wider frequency band, which brings great flexibility to the monitoring; secondly, at the power frequency or higher frequency, the capacitive part of the insulation leakage current is much larger than its resistive part, which makes the monitoring accuracy and sensitivity of the insulation capacitance higher. Fourth, based on the above ideas, this embodiment also provides an AC / DC integrated cable current sensor, which adopts the design concepts and goals of intensive, low power consumption, and miniaturization, forming an integrated sensor form with one sampling input and two independent signal outputs, which can simultaneously realize the monitoring of transient and steady-state fault currents, and more comprehensively understand the cable operation status in real time. The hardware structure of the AC / DC integrated cable current sensor is mainly composed of three main parts: coils, chips, and conditioning circuits; the AC / DC integrated cable current sensor can simultaneously realize real-time monitoring of AC and DC currents. Based on the above principles, this embodiment provides the following device prototype.

[0047] In this embodiment, the AC current Hall monitoring method adopts an open-loop mode, and monitors various types of cables through customizable magnetic coil inner diameters, and makes accurate judgments in the selection of Hall component materials and magnetic materials, thereby improving magnetic concentration and measurement linearity performance to solve the problem of poor linearity affecting measurement accuracy.

[0048] In this embodiment, the TMR DC micro-current monitoring method mentioned can monitor the cable insulation capacitance and resistance by measuring the cable insulation leakage current, thereby estimating the degree of insulation aging, and can realize the function of online monitoring of DC leakage current signals of 10kV cables.

[0049] In this embodiment, a highly integrated current sensor is provided, which adopts a dual-channel parallel acquisition mode and can simultaneously measure transient and steady-state fault information. Through anti-interference process design, the interference between the two signals and the bypass circuit is improved, thereby improving the accuracy of tiny current acquisition.

[0050] like Figure 1 As shown, this embodiment provides an AC / DC integrated cable current sensor, and the specific design ideas are as follows: The AC / DC integrated cable current sensor provided in this embodiment adopts an independent modular design for DC component detection and has two output lines, which respectively sample two analog signals as the basis for platform fault judgment; the two line signals are isolated, modularized, and shielded by a design mode, which greatly reduces sampling interference and ensures the accuracy of signal acquisition. The specific component designs are as follows: First, the selection of coils is crucial. The current value collected by it is also used as the signal source for AC and DC signal analysis. The material of the coil should have the characteristics of high magnetic permeability, small temperature coefficient, and high hysteresis coefficient. Magnetic materials with high initial magnetic permeability and good linearity can improve the sensitivity and accuracy of the current sensor. Generally, the materials with good magnetic concentration effects include silicon steel sheets, iron-nickel soft magnetic alloys, amorphous alloys, iron-based microcrystalline alloys and Permalloy. Microcrystalline and Permalloy are two magnetic materials with important application value. Microcrystalline is an amorphous magnetic material with a grain size of only nanometers; Permalloy is a crystalline alloy material with strong magnetism. They differ in magnetic properties, physical properties and applications. The magnetic properties of microcrystalline and Permalloy are one of their most basic differences. First, microcrystalline has a higher saturation magnetic induction intensity than Permalloy. Secondly, the hysteresis loss of microcrystalline is lower than that of Permalloy, showing better high-frequency characteristics. On the other hand, the iron loss of Permalloy is lower than that of microcrystalline, and the magnetic permeability is higher than that of microcrystalline. In this embodiment, iron-based permalloy is selected as the magnetic ring material after comprehensive consideration.

[0051] This coil adopts a double-layer structure design. The first layer (inner layer) collects the AC current value generated by the cable connector, and the second layer (outer layer) collects the leakage current generated by the cable injection signal. The clever design of the two-layer structure, on the one hand, realizes the current value collection of different performance parameters, and on the other hand, the outer shielding layer can shield and offset the large AC current through the inner coil, thereby improving the measurement accuracy of the outer layer's tiny current.

[0052] Second, chip selection and design: Hall current components use GaAs material (gallium arsenide), which has the best output linearity and can withstand a maximum temperature of 200°C. Design a double-sided wire-outlet packaged Hall element, which is deployed at the top of a layer of coils. The top has the best magnetic field gathering effect. Select the THS119 chip, and the thickness of the Hall element is generally no more than 2mm. The TMR chip selects the MAGIC2001 electromagnetic chip from Duochuang Technology, which can still ensure high measurement accuracy even in the presence of DC and harmonic components.

[0053] Third, modulation module design: The core of the modulation circuit includes temperature compensation circuit, signal conditioning circuit, amplification and zeroing circuit, etc. The temperature compensation circuit adjusts the op amp parameters according to the ambient temperature to compensate for the sensitivity of the internal TMR element. Design a temperature-sensitive voltage source to power the TMR element to compensate for the temperature drift error. For the output voltage of the TMR element in the order of mV, design a signal amplification circuit to amplify the signal to the order of V. Design the pre-stage signal amplification circuit and the secondary signal amplification circuit; the chip element adopts a bridge structure, and the initial values ​​of the four internal resistors cannot be guaranteed to be completely consistent due to the process. At the same time, affected by the surrounding stray magnetic field, the TMR element has a fixed output bias voltage, so a bias zeroing circuit is designed. Select the SX1278 communication transceiver chip with a built-in modem to achieve long-distance spread spectrum communication, good anti-interference, low current consumption, and use low-cost crystal oscillator and other materials, you can achieve a relatively high sensitivity, which can reach -148dBm.

[0054] This embodiment also provides a 10KV cable insulation aging monitoring method, which can be implemented using the AC / DC integrated cable current sensor provided in this embodiment, and the specific steps include: Collect the cable AC signal of the cable insulation and judge the transient aging degree of the cable insulation according to the sudden change of current amplitude in the flow signal; Synchronously collect the cable DC signal of the cable insulation and judge the steady-state aging degree of the cable insulation according to the cable DC signal; A leakage current variation trend curve is drawn based on the output cable DC signal of the cable insulation, so as to compare and analyze the steady-state aging degree of the cable insulation corresponding to different cable insulations according to the leakage current variation trend curve.

[0055] The cable DC signal of the cable insulation is collected by injecting a common mode DC current signal source and adopting a TMR electromagnetic detection method.

[0056] It can be seen that this method realizes comprehensive monitoring of the transient and steady-state aging degree of cable insulation by synchronously collecting the AC and DC signals of the cable. The AC and DC component detection adopts an independent modular design. This method designs two output lines and samples two analog signals respectively as the basis for platform fault judgment. The two line signals are isolated, modularized, and shielded by the design mode, which greatly reduces the sampling interference. This method improves the real-time and accuracy of monitoring.

[0057] In this embodiment, an experimental study was conducted on the above-mentioned integrated cable current sensor and 10KV cable insulation aging monitoring method, and the specific implementation process is as follows: The AC / DC integrated cable current sensor is installed and deployed at the 10kV cable joint to measure the ground current and common-mode leakage current at the same time. It is used to monitor the DC leakage current of the high-voltage feeder and the AC current of the cable sheath in real time in the power supply and distribution system. The two current components exist simultaneously in the high-voltage feeder line.

[0058] Step 1. In the AC current measurement experiment, simulate the injection of 12kV / 50Hz high-voltage signal, connect the AC output end of the integrated current sensor to the computer, and read the AC current output amplitude signal. Generally, when an overvoltage occurs, the cable will have a short circuit breakdown phenomenon. The transient aging degree of the cable insulation is judged based on the AC current output amplitude signal.

[0059] Step 2. In the cable common-mode leakage current measurement experiment, the 380V / 433V three-phase voltage regulator supplies power to the Y-shaped connected load resistor through the three-phase test cable segment to generate a differential-mode load current IDM; changing the output voltage of the three-phase voltage regulator can change the magnitude of the differential load current. At the same time, the 220V / 250V single-phase voltage regulator is connected to the common-mode current adjustment resistor through the common-mode current conductor to generate a simulated common-mode leakage current. The magnitude of the common-mode leakage current can be changed by changing the output voltage of the single-phase voltage regulator. The common-mode current conductor is placed close to the surface of the three-phase cable segment, and the two pass through the sensor prototype with the above structural design. The DC output end of the AC / DC integrated cable current sensor is connected to a computer to read the current amplitude signal. The capacitive leakage current and resistive leakage current amplitudes of the cable at different degrees of insulation aging under the power frequency are as follows: Figure 2 and Figure 3 As shown: Figure 2 It shows that the insulation capacitive leakage current gradually increases with the aging degree of the cable. Figure 3It shows that the resistive leakage current also gradually increases with the increase of cable aging degree; and in the whole process of cable aging, the insulation capacitive leakage current is much greater than the resistive leakage current. In the early aging process of the cable, the insulation capacitive leakage current increases significantly, while the resistive leakage current changes little. When the aging degree is more serious, although the insulation resistive leakage current increases rapidly, it is still one order of magnitude different from the capacitive leakage current. Therefore, the capacitive leakage current accounts for the vast majority of the insulation leakage current under the power frequency, and the insulation capacitance can be effectively monitored by measuring the insulation leakage current.

[0060] In summary, the present invention provides an AC / DC integrated cable current sensor and a 10KV cable insulation aging monitoring method, which have the following advantages over the existing cable monitoring technology: First, the present invention proposes a method for monitoring the short-circuit current of a 10kV cable using an AC current Hall. An open-loop mode is adopted to monitor various types of cables through the customizable inner diameter of the magnetic coil. Accurate judgments are made in the selection of Hall component materials and magnetic materials, thereby improving the magnetic concentration and measurement linearity performance and solving the problem of poor linearity affecting measurement accuracy.

[0061] Second, the present invention proposes to adopt the TMR DC micro-current monitoring method, which can monitor the cable insulation capacitance and resistance by measuring the cable insulation leakage current, and can realize the function of accurately monitoring the DC leakage current signal of the 10kV cable online.

[0062] Third, the present invention proposes an AC / DC integrated cable current sensor, which simultaneously realizes a method for collecting transient and steady-state fault information of a 10kV cable. The AC / DC component detection is independently modularized internally, and two outgoing lines are designed to sample two analog signals respectively as a basis for platform fault judgment. The two line signals are isolated, modularized, and shielded by a design mode, which greatly reduces sampling interference.

[0063] The above embodiment is only one of the implementation methods that can realize the technical solution of the present invention. The scope of protection claimed by the present invention is not limited only to this embodiment, but also includes changes, replacements and other implementation methods that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention.

Claims

1. An AC / DC integrated cable current sensor, characterized in that: It includes a sensor body and a cable AC signal acquisition module and a cable DC signal acquisition module arranged in the sensor body; The cable AC signal acquisition module is used to collect the cable AC signal to determine the transient aging degree of the cable insulation according to the sudden change in the current amplitude of the cable AC signal; The cable DC signal acquisition module is used to acquire the cable DC signal to determine the steady-state aging degree of the cable insulation according to the cable DC signal; The cable AC signal acquisition module and the cable DC signal acquisition module share a sampling input terminal, and the collected cable AC signal and cable DC signal are output independently.

2. The AC / DC integrated cable current sensor according to claim 1, characterized in that: The sensor body includes a coil and a conditioning module; the receiving ends of the cable AC signal acquisition module and the cable DC signal acquisition module are respectively connected to the coil, and the output ends are respectively connected to the conditioning modules; the conditioning module is used to condition and output the collected cable AC signal and cable DC signal.

3. The AC / DC integrated cable current sensor according to claim 2, characterized in that: The coil adopts a double-layer structure; the inner coil is connected to the cable AC signal acquisition module, which is responsible for acquiring the cable AC signal generated by the cable connector; the outer coil is connected to the cable DC signal acquisition module, which is responsible for acquiring the cable DC signal generated by the cable injection signal; the coil is made of iron-based microcrystalline alloy or Permalloy material.

4. The AC / DC integrated cable current sensor according to claim 2, characterized in that: The cable AC signal acquisition module adopts a Hall sensing and sampling chip, which is arranged on the top of the inner coil; the cable DC signal acquisition module adopts a TMR chip, which is electrically connected to the outer coil.

5. The AC / DC integrated cable current sensor according to claim 4, characterized in that: The Hall sensing and sampling chip is made of GaAs material and uses THS119 chip; The TMR chip adopts MAGIC2001 electromagnetic chip.

6. The AC / DC integrated cable current sensor according to claim 4, characterized in that: The conditioning module includes a temperature compensation circuit, a signal conditioning circuit, and an amplification and zeroing circuit; The temperature compensation circuit is used to adjust the operational amplifier parameters according to the ambient temperature to compensate for the sensitivity of the TMR chip; The signal conditioning circuit includes an AC component conditioning circuit connected to the Hall sensing and sampling chip and a DC component conditioning circuit connected to the TMR chip, which is used to improve the spread spectrum communication distance; The amplification and zeroing circuit is used to amplify the signals collected by the Hall sensing and sampling chip and the TMR chip and to zero the TMR chip.

7. The AC / DC integrated cable current sensor according to claim 1, characterized in that: The sensor uses an open-loop mode to monitor cable insulation; the acquisition principle of the cable AC signal acquisition module is based on the following formula: In the formula, is the output voltage signal; R is the Hall coefficient; I is the driving current of the Hall element; B is the magnetic field strength of the magnetic ring air gap.

8. A 10KV cable insulation aging monitoring method, characterized in that: The AC / DC integrated cable current sensor according to any one of claims 1 to 7 comprises: Collect the cable AC signal of the cable insulation and judge the transient aging degree of the cable insulation according to the sudden change of current amplitude in the flow signal; The cable DC signal of the cable insulation is collected synchronously, and the steady-state aging degree of the cable insulation is determined according to the cable DC signal.

9. The 10KV cable insulation aging monitoring method according to claim 8, characterized in that: By injecting a common-mode DC current signal source, the cable DC signal of the cable insulation is collected using the TMR electromagnetic detection method.

10. The 10KV cable insulation aging monitoring method according to claim 8, characterized in that: Also includes: A leakage current variation trend curve is drawn based on the output cable DC signal of the cable insulation, so as to compare and analyze the steady-state aging degree of the cable insulation corresponding to different cable insulations according to the leakage current variation trend curve.

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